The present invention relates to a belt printing mechanism comprising endless belts which are disposed parallel to each other and which on their outer surfaces carry print types and are each led round an adjusting wheel and a star wheel rotatable about a shaft, and a catch mechanism for preventing a free rotation of the star wheels which is held in positive engagement with the star wheels and holds the latter in predetermined detent positions.
Such a belt printing mechanism is already known. In the latter printing mechanism the individual type belts can be adjusted by rotating the particular associated adjusting wheel so that desired print types at the type belt outer surfaces come into a predetermined printing position. On rotation of the adjusting wheel the type belt is entrained by the adjusting wheel and the associated star wheel about which the type belt is also led also rotates about its axis. A printing type on the type belt is in the printing position when it is disposed on the peripheral surface of the star wheel remote from the adjusting wheel. For printing multi-digit characters print types of a plurality of adjacently disposed type belts must be brought into the printing position. On rotating of the adjusting wheels for obtaining the desired adjustment of the type belts it must be ensured that the printing position of the types to be printed must be reached as exactly as possible. Slightly different adjustments of the types to be printed will result in printing types producing imprints which do not all lie on the same line height. To facilitate the exact adjustment of the printing types in the printing position for the operator a catch mechanism is provided which prevents the star wheels from being able to rotate freely. Said catch mechanism is so constructed that it holds each star wheel in a predetermined position and permits rotation of the star wheels only after overcoming a certain force. With the four-cornered star wheels employed the catch mechanism acts positively on the peripheral surface portion of the star wheels which is opposite the peripheral surface portion on which the print types are disposed in the printing position. By rotating the adjusting wheels the operator can move the type belts and thus also the star wheels against the force exerted by the catch mechanism but he can feel that before each rotation of a star wheel through 90.degree. a certain force must be overcome. These force peaks which can be felt by the operator on rotating an adjusting wheel facilitate the correct positioning of the print types to be printed.
In the known printing mechanism as catch mechanism for each star wheel a push member is provided which by means of a spring is held in engagement with a peripheral surface portion of the associated star wheel. On rotation of the star wheel a corner thereof pushes the push member back against the spring force which leads to a noticeable increase in the force necessary for rotating the star wheel. The already mentioned force peaks then occur whenever the push member is pushed back by a star wheel corner against the spring force. To obtain the spring force a rubber strip is disposed beneath the push member provided for the individual star wheels and said strip can yield when the push member is pushed back by a star wheel corner. The catch mechanism in the known belt printing mechanism consists of numerous individual parts which must be made with close tolerances. These numerous individual parts are not only expensive to manufacture but also require a relatively great amount of time for installment into the belt printing mechanism.
The objective of the present invention is to further develop the belt printing mechanism of the type outlined at the beginning so that with simple and cheap means an exact locating of the print types to be printed can be achieved.
According to the invention this objective is achieved in that the catch mechanism comprises for each star wheel a spring tongue which contacts the portion of the peripheral surface of the star wheel extending between two adjacent corners of the star wheel at at least two spaced-apart points and the plane of which forms an acute angle with the plane in which the star wheel rotates about its shaft.
The spring tongue used in the belt printing mechanism according to the invention for each star wheel fulfills simultaneously the function of holding the star wheel in a desired position and the function of producing the force peaks which can be felt by the operator on adjustment of the type belts. In this manner the use of different components for fulfilling these two functions is obviated.
Other objects, advantages and novel features of the present invention will be apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.